Signaling system



1943- w. w. FRITSCHI 2,332,907

SIGNALING SYSTEM Filed April 23, 1942 g R F/G. B L/ /o I 50 L2 5% ,L/ 5%ML 57/ I III 3 K,

RECTIFIER H T F/2 I I 572 F/GZI Ill '2 a4 65 as 63 I AMR FILTER AMRINVENTOR I4. W FRI TSCH/ fflinaa A 7' TOR/VE V Patented Oct. 26, 1943 lsThisinvention relates to signaling systems and particularly to systemsin which alternatingcurrent of voice frequency is utilized to transmitsignals over telephone lines.

' Objects of the :invention are an increase in the reliability ofvoicefrequency signaling systems and the prevention of false signaloperations due to voice currents occurring in telephone lines i in t tThis invention is asignaling system in which the-alternating current ofvoice frequency transmitted'as a signal over a lineto operate a signalreceiver is anl asymmetric current, that is, currentlin which theamplitude of the positive half cycles differ substantially fromtheamplitude of thenegative half cycles thereby enabling a signaloperation responsive to signaling current but not to voicecurrent of thesignaling frequency, voice currents ,being only slightly-asymmetric ascompared'with the signaling current. t

UNITED ,STATES A f 1 4 1 H g SIGNALING SYSTEM/1 a Walter W. Fritschi,Manhasset, N. Y., assi'gnonto Bell Telephone Laboratories, Incorporated,[I New YQI'LNQY acorporation of NewgYork M v u v Application April 23,1942, swarm. 440,140 a 9Claims. 1794) l 20 Features of the invention arethe provision of signal current supply and transmitting means and theprovision of a signal receiver adapted toefiect asignal operationresponsive to asym-J metric signalingcurrent without effecting a signaloperation responsive to voice currents of thesignaling frequency, thevoice currents being considerably more symmetrical in wave form thansignaling current. l r t l Another featureof the invention is the use ofarectifier or detectorin a signal transmitter to render the signalingcurrent asymmetrical in its wave formtoenableits detection asdistinguished from voice or other wave form; r t t A. W. :Horton, Jr.,and M. A. Logan, Serial-No.

440,138, filed April 23,1942, also covers a system inrwhich thedifference in wave formbetween signal currents and speech currents isutilized speech to prevent'signal operation in response to currents. M t

wAnjother feature is the insertion of a transformer with a polarizedcore in the signal trans-' mission path of a voice frequency signalingcircuit to render the signaling current transmitted" therethroughsufficiently asymmetrical in its wave form to be distinguishable fromvoice or other currents ormore symmetrical wave form. A; clear andcomplete understanding of the currents of more symmetrical l l l 40 lThe-zeopending application of S. M. Babc'ock,

inventionwill be facilitated by considering a signaling system arrangedin accordance with the variousfeaturesof the invention, one such systembeingrepresented schematically in the draw h ing which forms a partofthis specification; Referring tothe drawing which consists of fourFig.1 represents a system comprising subscribers telephone stations Aand B and lines: LI and L2 and a toll line TL to which are connected afortransmitterSTl for transmitting signals over:

line TL to thesignal receiver SR. 1

The line TL is a telephone line over which voice currents andsupervisory and selective signals are transmitted;alternating currentwithin thevoice frequency range being employed for the transmission ofthe various signals; One end of the line TL is connected through arepeating coil II] to a signaltransmitter STI and the otherend through arepeating coil "5!! tea signal receiver SR. If arranged for two-waysignaling the line TL will also be "connected through coil lotto asignal receiver similarto SR and through cell 50 to a'signal transmittersimilar to STi'. 'A call-1 ing station A andline Ll maybe connected to30' one endqofr-line I'L by manually operated or impulse controlledswitching mechanism and the other end of line TLmay then be; connectedunder the control of selective impulses to a called, line L2 and stationB. Reference may be had to the patent to King et al. No. 2,209,777granted July 30, 1940 for a description of a systemco-mprising tolllines and impulse controlled switching mechanism for establishingconnections. The signal transmitter STl comprises a signal currentgenerator G which generates alternating current of a desired frequencycharacteristic within the voice frequency range, a transformer Tlthrough which the signaling potentials are impressed across therepeatingcoil Ill, asignal' sending device KI, and a half-wave rectifier R1,,

or unidirectional impedance element for render-, ing the current, whichis transmitted over line TL to the receiver SR upon closure of thecontacts of device Kl, asymmetrical in that the amplitude of the halfcycles of one polarity will be substantiallylarger than the half cycles,of'

the other polarity. A likei polarization offthe' signaling current isefiected'in the alternative mitter ST2, a half-wave rectifier isconnected show signal transmitters STZ in parallel with the generator Ginstead of in series with the generator as in the transmitter STI.through which the signaling potentials are impressed across repeatingcoil in has a polarized core to render the signaling current asymmetric.The polarization of the core may be efiected by energization of anotherwinding. (not shown) by direct current. And transmitter STE, thesignaling potentials are applied through atrans In transmitter ST3, thetransformer T3 former 42, vacuum tube detector 40 and transformer T4,the detector being biased to render the current transmitted throughtransformer "T4 asymmetric in the desired degree.

The signal receiver SR; comprisesan input.

winding of said first control relay, a detector re- .sponsive to thenegative half cycles of current in transformer 53, three-element vacuumtubes 58 and 59 acting as amplifiers, a differential relay said inputcircuit for energizing another winding of said first control relay, saidwindings being differentially energized to prevent the oper- "ation ofsaid first control relay in response to 60, and a vacuum tube 62 havinga cathode, a l control gridand an anode which cooperate to form anamplifier and having two additional anodes which cooperate with thecathode to form two half-wave rectifiers for cppositelypolarizing thepotentials applied to the grids of tubes '58 current of substantiallysymmetrical wave form in said input circuit and to effect operation ofsaid first control relay in response to signaling current insaidinputrcircuit, a second control relay; means. comprising amplifierand detector and. 59; .The receiver. SR, further comprises a transformer63; a band-pass filter 64, anramplifier 65,-an amplifier :detector 66, arelay '6! for-leperation in response to current of either symmetricaloriasymmetric'al waveform in the input circuit of transformer 53, :and asingle relay 69 :controlled by relays landfill, I i

1 Voice current transmitted over line Ll from station A and signalingcurrent from transmit ter, S'Il are transmitted through'repeating coill0,ft011 line 'IfL,'repeating coil 50, conductors '51. and52, andtransformer 53 thereby impressing an alternatingpotential onthetcontrolgrid of tube 6i! and impressing potentials" derived from the positiveand negative half 'cycles of the current in the primary winding oftransformer '53v on'the grids of amplifier tubes 58 and 59; respec,

tively. The current :in the .output circuit of amplifier tube 58energizes the upperiwinding of ,relayifiil and the current .in theoutput; circuit of amplifier tube 59 energizes the lower. of relay fill,these windings being thereby different-iall'yi energized: "If thecurrent in lineTL is symmetrical in its wave form, relay to does notsymmetrical or asymmetrical in wave f rm; the

alternating potential appl'ied to the control grid oftube 62 causes thetransmission of an ampli fied current through transformer 63 'to theinput side of band-pass filter {6-4. This filter is tuned meansresponsive to current in'said input circuit for operatively.energizingsaid second control relay, and axsignal'relayresponsive onlyto the simultaneous operation of: both. of said control'relays.

2. In a 'signaling system, :a line, means for transmitting signalscomprising alternatingcurrentwof voice frequency'over said line, meansrendering." said signaling scurrent asymmetrical in waveform,iandiasignalreceiver for responding to signals transmitted over.said line, said receivercomprising a detector responsive to alterhatingcurrent of both symmetrical and asym only to OHI'IBIItLWhiChi Sasymmetrical in wave to pass current of thegsi-gnaling'frequencyftlnecurrent thus transmitted being amplified by am-' pl'i'fier -65, vfurtheramplified and rectified by ampli fier detectorffifi to energize thewinding of relay '67. Thus rel'ay jfil is operatively energized bycurrent of the signalingfrequency of either symmetrical or asymmetricalwave form. QIf this current is signaling current it is sufiicien'tlyasymmetrical. in Wave form to operate relayffifi. inadditio'ntooperating relay 6''; the operation of both of relays '61 and beingeffective to,

operate signal relay 59 to e'fie'ct anydesired .sig naling operation,"If; however, the current in :line

TL is voicecurrent which is symmetrical en my slightly asymmetrical in'wave form,'the ienergi; zation of the two windings of relay 613'. willso closely balance each other that relaylifl does not operate;f andftheoperationfof relay S'I alone, in

form in larger degree-than are'i voice currents,-

and a signal deviceunder the joint control-of said detectors, saiddevicebeingnperated in response to signaling current but not in responsetovoice current brother; currents ofsubstantially symmetricalwavelform.:t- I v 3. In 'a signalirlg' system in which signals aretransmitted by alternating-current which are withinpthevoice frequency.rang-e'and asymmet'-' ricalzin waveform. to a substantially greater degree than :are voice currentsa' signal receiver comprisinga'n inputcircuit, a detector for detecting thespositive half cycles-or current insaid input'circuit, a detector for detecting the negative half cycles ofcurrent in said input circuit, a first control relay, one Winding ofsaid relay connected in thelzoutput 'circuit iof one of said detectorsand another winding of said relay connectedtin the output circuit of theother 0f said detectors, said windings :being differentially ener gizedby the currents in the outputvcircuitsof said detectors thereby toenable operation of the relay responsive to asymmetrical.signaiingscu-rrent in said input circuit ibut non-responsive tovoicepur-rents orzother currents whichlare sub stantiallysymmetricali-in wave form, a second control relay; means :for operating.sazld second control relay responsive to current in said input circuitof either symmetrical or asymmetrical wave form, and a ,signal' relaycontrol of said control relays.

In a signaling system-in which signals are under the joint transmittedbyalternatmg currents which are e-fneanencyrang'e rand asymmetri I ;-toasubstantially greater degree rrents, a signal receiver com-- within thecal in wave l than. are voice prising an input circuit, two detectortubes connected to said input circuit, rectifier means in the gridcircuit of one of said detector tubes rendering said tube responsiveonly to the positive half cycles of current in said input circuit,rectifier means in the grid circuit of the other of said detector tubesrendering said tube responsive only to the negative half cycles ofcurrent in said input circuit, a relay having two windingsconnecteddifferentially in the output circuits of said two detectorsthereby to effect operation of said relay only in response to current ofasymmetric Wave form in said input circuit, an amplifier connected tosaid input circuit, a relay operatively controlled by said amplifierresponsive to current of symmetrical or asymmetrical wave form in saidinput circuit, and a signal circuit closed by the operations of both ofsaid relays responsive to signaling current in said input circuit.

5. In a signaling system in which signals are transmitted by alternatingcurrent of a particular frequency within the voice frequency range andasymmetrical in wave form to a substantially greater degree than arevoice currents, a signal receiver comprising an input circuit, adetector for detecting the positive half cycles of current in said inputcircuit, a detector for detecting the negative half cycles of current insaid input circuit, a relay having two windings individually anddifferentially connected in the output circuits of said detectors toeffect the operation of said relay in response to current of wave formwhich is asymmetrical in a larger degree than are voice currents,another relay, means comprising amplifying means, a band-pass filter anddetector means connecting said other relay to said input circuit, saidfilter tuned to said particular frequency, whereby said other relay isoperatively responsive only to current of said particular frequency, andsignal means operated only by the operation of both of said relaysresponsive to signaling current in said input circuit.

6. In a signaling system, a line, means for transmitting signalscomprising alternating current of voice frequency in said line, saidmeans comprising a half-wave rectifier, a source of alternating current,and a signal sending device connected in series for transmittingsignaling currents of wave form asymmetrical to a substantially greaterdegree than are voice currents,

and a signal receiver connected to saidline, said receiver comprising adetector responsive to alternating current of both symmetrical andasymmetrical wave form transmitted over said line, an

asymmetry detector operatively responsive only to current which isasymmetrical in larger degree transmittingsignals comprising alternatingcurrent of voice frequency over said line, said means comprising asource of alternating current and a signal sending device connected inseries and a half-wave rectifier connected in parallel with said sourceand device, the signaling current thus transmitted over said line beingasymmetrical in wave form to a greater degree than voice cur rents, anda signal receiver connected to said line,

i 7. In a signaling system, aline, means for relay responsive to currentof symmetrical or asymmetrical wave form in said input circuit,

and signal means operated only in response to the operation of both ofsaid relays.

8. In a signaling system, a line, means'for transmitting signalscomprising alternating current of voice frequency over said line, saidmeans comprising a source of alternating current and a transformerhaving a core of saturated magnetic material effective to polarize thecurrent in the secondary winding of said transformer, the signalingcurrent thus transmitted over said line being asymmetrical in wave formto a greater degree than voice currents, and a signal receiver connectedto said line, said receiver comprising an input circuit, a detector fordetecting the positive half cycles of current in said input circuit, adetector for detecting the negative half cycles of current in saidoutput circuit, a relay having two windings individually anddifferentially connected in the output circuits of said detectors toeifect the operation of said relay in response to current of wave formwhich is asymmetrical in larger degree than voice currents, anotherrelay, means comprising amplifying and detecting means connected to saidinput circuit for operatively energizing said other relay responsive tocurrent of symmetrical or asymmetrical wave form in said input circuit,and signal means operated only in response to the operation of both ofsaid relays.

9. In a signaling system, a line, means for transmitting signalscomprising alternating current of voice frequency over said line, saidmeans comprising a source of alternating current and a signal sendingdevice in series and comprising a vacuum tube detector for polarizingthe current transmitted over said line, the signaling current thustransmitted over said line being asymmetrical in wave form to a greaterdegree than voice currents, and a signal receiver connected to saidline, said receiver comprising an input circuit, a detector fordetecting the positive half cycles of current in said input circuit, adetector forv detecting the negative half cycles of current in saidoutput circuit, a relay having two windings individually anddifferentially connected in the output circuits of said detectors toeffect the operation of said relay in response to current of wave formwhich is asymmetrical in larger degree than voice currents, anotherrelay, means comprising amplifying and detecting means connected to saidinput circuit for operatively energizing said other relay responsive tocurrent of symmetrical or asymmetrical wave form in said input circuit,and signal means operated only in response to the operation of both ofsaid relays.

WALTER W. FRITSCHI.

